Besides the transmission of already digitized, or rectangular incremental signals, known incremental position measuring systems also make the transmission of sine-shaped analog incremental signals to a downstream arranged evaluation unit possible. In this case the analog incremental signals can be generated in the most varied manner, for example by optical, magnetic, inductive or capacitive scanning of a physically embodied scale graduation. Besides this, the analog, position-dependent incremental signals can also be generated by an interferometer, in which case the light wavelength, or respectively appropriate fractions thereof, instead of a physical scale structure, constitutes the graduation normal. It would also be conceivable to employ fractions of other wave forms as graduation normals, for example when using microwaves, acoustical waves, etc. in the same way.
Processing of the transmitted analog incremental signals is initially performed by the evaluation unit, for example, a further division in the form of an interpolation. The transmission of analog incremental signals from the position measuring system to the evaluation unit offers some advantages, such as a low transmission frequency with constant measuring steps, as well as a relatively high permissible displacement velocity even at small measurement steps.
If, however, position measuring systems of high resolution and correspondingly short signal periods are employed, for example, laser interferometers or interferentially operating optical position measuring systems, a number of problems can result in connection with the transmission of analog incremental signals. For example, if the signal periods of such position measuring systems lie in the range of approximately 0.5 .mu.m, high signal frequencies of the analog incremental signals on an order of magnitude of approximately 2 MHz already result at relatively slow displacement velocities of 1 m/s. Not all evaluation units are capable of processing such high-frequency analog incremental signals. Problems furthermore arise in connection with the transmission of high-frequency incremental signals over large distances. If there is interference with the signal transmission, errors in the position determination by the evaluation unit result. For example, in order to increase resolution, in particular, in the case of signal interpolation being performed on the part of the evaluation unit, ideal sine-shaped incremental signals from the position measuring system is a prerequisite.
Furthermore, in connection with various applications, different demands are sometimes made on the resolution of the analog incremental signals provided by the position measuring system. While for high displacement velocities no extreme exactness of the position determination is, as a rule, required, at slower relative velocities higher demands are usually made on the available resolution of the analog incremental signals of the position measuring system.